The Pakistani journalist Syed Saleem Shahzad knew he was a marked man. Mr. Shahzad, who covered national security and terrorism, had received repeated threats from Pakistan’s powerful spy agency. Yet he courageously kept doing his job — until somebody silenced him. His body, his face horribly beaten, was buried on Wednesday.

Suspicion inevitably falls on Inter-Services Intelligence, Pakistan’s chief intelligence agency. For the sake of justice, and the shredded credibility of Pakistan’s government, his murderers must be found quickly and held accountable.

Mr. Shahzad disappeared from Islamabad on Sunday, two days after he published an article suggesting a militant attack on a naval base in Karachi was retaliation for the navy’s attempt to crack down on Al Qaeda militants in the armed forces. American analysts doubt an Al Qaeda cell infiltrated Pakistani security, but they have long worried about individual sympathizers.

Whatever the case, the attack humiliated the ISI and the armed services. They were already fending off allegations that they sheltered Osama bin Laden and criticism for failing to stop the American raid that killed him.